A wireless communication system typically includes a plurality of Base Stations (BSs) and a plurality of Mobile Stations (MSs). Each BS of the plurality of BSs has a range of coverage up to which the BS can transmit data packets. A BS transmits data packets within transmission frames to each MS of the plurality of MSs through a Downlink (DL). Similarly, each MS transmits data packets to the BS through an Uplink (UL).
A transmission frame transmitted by a BS to a MS of the plurality of MSs includes resource allocation information associated with the MS. The resource allocation information includes a DL MAP and an UL MAP specifying DL and UL resource allocation associated with the MS to receive and transmit data packets respectively. The DL and UL MAPs are transmitted in each transmission frame. The resources include frequency and time slots in the transmission frame. The DL MAP and the UL MAP thus schedule the communication between the BS and the plurality of MSs. Transmitting the DL and UL MAPs in each transmission frame leads to significant overhead in the wireless communication system.
For applications generating periodic data packets, the resource requirements of an MS can be pre-determined. For example, if periodic data is generated by the application with a period of four transmission frames, the BS persistently allocates resources to the MS in every fifth transmission frame. As a result, the resource allocation information corresponding to the persistent resource allocation is transmitted in the first transmission frame and need not be transmitted in every fifth transmission frame. This reduces the amount of resource allocation information that needs to be sent to each MS in the subsequent transmission frames.
However, the BS may change the persistent allocations if, for instance, a quality of communication channel between a MS and the BS either improves or deteriorates. For example, an MS using a first Modulation and Coding Scheme (MCS) corresponding to a quality of a communication channel may be switched to a second MCS when the quality of the communication channel changes. This switch is indicated to the MS by the BS by transmitting additional relevant resource allocation information to the MS. Thus, each such change from the persistent allocations requires additional resource allocation information to be included in the DL MAP and UL MAP thereby increasing the overhead in the wireless communication system.
Further, the departure of an MS from a coverage area of a BS leads to de-allocation of resources initially allocated to the MS. The de-allocation of resources results in the formation of one or more unused slots i.e., holes in a transmission frame. These un-used slots may be allocated to one or more MSs of the plurality of MSs communicating with the BS by shifting the resource allocations of the other MSs so as to utilize the holes. Such changes in resource allocations either needs to be communicated to each MS thereby incurring additional DL and UL MAP overhead or has to be inferred by each MS whenever there is de-allocation information in the DL or UL MAP.
In the wireless communication system, due to frequent changes in communication channel quality, it is likely that a MS may be unable to decode the DL MAP or UL MAP. The DL MAP or UL MAP may include either a new persistent allocation or de-allocation of a previous persistent allocation associated with the MS. Consequently, the MS may not recognize that the BS has changed resource allocation for the MS in the subsequent frames. Thus, the MS may incorrectly attempt to receive on the DL or transmit on the UL. This results in a loss of transmission throughput on either the DL or the UL.
Therefore, there is a need for a method and an apparatus for reducing DL MAP and UL MAP overhead and efficiently utilizing communication resources, in the presence of MAP errors introduced by frequent changes in communication channel quality.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the invention.